According to the prior art automatic transmissions, especially those for motor vehicles, comprise planetary gear sets which are shifted by means of frictional or shift elements such as clutches and brakes, and are usually connected to a starting element that is liable to slip and is optionally provided with a bridging clutch, such as a hydrodynamic torque converter or a flow clutch.
In general, vehicle transmissions of planetary structure have already been described many times in the prior art and undergo continual further development and improvement. Such transmissions should demand little construction effort and expenditure, in particular a small number of shift elements, and should avoid double shifts when operated in a sequential shift mode so that during shifts in defined gear groups, in each case only one shift element is changed, i.e. to shift from one gear to the respective next-higher or next-lower gear, in each case only one of the shift elements engaged at the time has to be disengaged and only one of the shift elements disengaged at the time has to be engaged.
For example, an automatic transmission of that type is known from WO 2006/074707 A1 by the present applicant. This multi-stage transmission of planetary design comprises a drive input shaft, a drive output shaft, four planetary gear sets, at least eight rotating shafts and five shift elements, preferably two brakes and three clutches, such that a carrier of the fourth planetary gear set and the drive input shaft are connected in a rotationally fixed manner to one another and form the first rotating shaft of the transmission, and such that a carrier of the third planetary gear set and the drive output shaft are connected in a rotationally fixed manner to one another and form the second rotating shaft of the transmission. Furthermore, a sun gear of the first planetary gear set and a sun gear of the fourth planetary gear set are connected in a rotationally fixed manner to one another and form the third rotating shaft of the transmission, and a ring gear of the first planetary gear set forms the fourth rotating shaft of the transmission. Further, a ring gear of the second planetary gear set and a sun gear of the third planetary gear set are connected in a rotationally fixed manner to one another and form the fifth rotating shaft of the transmission, a carrier of the first planetary gear set and a ring gear of the third planetary gear set are connected in a rotationally fixed manner to one another and form the sixth rotating shaft of the transmission, and a sun gear of the second planetary gear set and a ring gear of the fourth planetary gear set are connected in a rotationally fixed manner to one another and form the seventh rotating shaft of the transmission; the eighth rotating shaft of the transmission is formed by a carrier of the second planetary gear set. With a transmission designed in this way eight forward gears and one reverse gear can be obtained.
Regarding the connection of the five shift elements to the various elements of the planetary gear sets and to the drive input shaft of the transmission, according to WO 2006/074707 A1 it is proposed that the first shift element is arranged in the force flow between the third shaft and a housing of the transmission, the second shift element is arranged in the force flow between the fourth shaft and the transmission housing, and the third shift element is arranged in the force flow between the fifth and the first shafts. Furthermore, the fourth shift element is arranged in the force flow between the eighth and the second shafts or, however, between the eighth and the sixth shafts, whereas the fifth shift element is arranged in the force flow either between the seventh and the fifth shafts, or between the fifth and the eighth shafts. By virtue of these various kinematic couplings of the shift elements to the various shafts of the transmission an entire transmission family is obtained.